A neutron imaging diagnostic has recently been commissioned at the National Ignition Facility (NIF). This new system is an important diagnostic tool for inertial fusion studies at the NIF for measuring the size and shape of the burning DT plasma during the ignition stage of Inertial Confinement Fusion (ICF) implosions. The imaging technique utilizes a pinhole neutron aperture, placed between the neutron source and a neutron detector. The detection system measures the two dimensional distribution of neutrons passing through the pinhole. This diagnostic has been designed to collect two images at two times. The long flight path for this diagnostic, 28 m, results in a chromatic separation of the neutrons, allowing the independently timed images to measure the source distribution for two neutron energies. Typically the first image measures the distribution of the 14 MeV neutrons and the second image of the 6-12 MeV neutrons. The combination of these two images has provided data on the size and shape of the burning plasma within the compressed capsule, as well as a measure of the quantity and spatial distribution of the cold fuel surrounding this core.
The fraction of light backscattered from plasmas produced by 10.6-μm laser light focused on polyethylene slab targets is ∼5% of the incident for intensities between 1013 and 1015 W/cm2. Time-integrated measurements of the spectrum of backscattered light near 10.6 μm are presented.
We present a design study of PIXSIC, a new B^+ radiosensitive microprobe implantable in rodent brain dedicated to in vivo and autonomous measurements of local time activitycurves of beta radiotracers in a small (a few mm^3 ) volume of brain tissue. This project follows the initial β microprobe previously developed at IMNC, which has been validated in several neurobiological experiments. This first prototype has been extensively used on anesthetized animals, but presents some critical limits for utilization on awake and freely moving animals. Consequently, we propose to develop a wireless setup that can be worn by an animal without constraints upon its movements. To that aim, we have chosen a Silicon-based detector, highly β sensitive, which allows for the development of a compact pixellated probe (typically 600 X 200 X1000 μm^3), read out with miniaturized wireless electronics. Using Monte-Carlo simulations, we show that high resistive Silicon pixels are appropriate for this purpose, assuming that the pixel dimensions are adapted to our specific signals. More precisely, a tradeoff has to be found between the sensitivity to β^+ particles and to the 511 keV γ background resulting from annihilations of β^+ with electrons. We demonstrate that pixels with maximized surface and minimized thickness can lead to an optimization of their β^+ sensitivity with a relative transparency to the annihilation backgroun
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